The present invention relates to a speed control apparatus for use with an electric sewing machine.
In recent years, sewing machines of the conventional type in which the rotative speed control thereof is effected by treading action have been largely superseded by a sewing machine so designed that said control is effected by button operation. Generally, the sewing machine in which the rotative speed is controlled by button operation as described above comprises, as shown in FIG. 1, a plurality of speed selection buttons A for selecting desired rotative speeds of the sewing machine, and a stop button B for stopping the sewing machine, said buttons A and B being juxtaposed on the right-hand side of the machine body, the arrangement being such that depressing a predetermined one of the speed selection buttons associated with respective preset speeds gives a desired speed to the machine and that when it is desried to stop the machine, this is achieved by depressing the stop button B included in said group of buttons. However, in sewing operation by machine, the operator's two hands are placed on the cloth, with his or her eyes directed on the tip of the sewing-machine needle, so that, with said speed selection buttons A and B located on the right-hand side of the machine body remote from the tip of the needle, when the sewing approaches the terminal stitch portion which is most difficult to work, it is necessary for the operator not only to shift one of his or her two hands placed on the cloth to the stop button with the proper timing for stopping the machine but also to turn his or her eyes away from the needle in order to ascertain the position of the button. Such operation makes it more difficult and complicated for unskilled persons to do the sewing. Further, in the sewing machine disclosed in Japanese Pat. Lay-Open No. 112,645/73, as show in FIG. 2, a lever D is provided on the needle attaching side of the machine arm C for starting and stopping the drive motor while speed selection buttons E alone are located on the right-hand side of the machine arm C, the arrangement being such that when it is desired to start the machine, this is achieved by first depressing the speed selection button which is associated with a desired rotative speed and then turning on the lever D and that the machine can be stopped by turning off the lever D. Althugh this machine may be said to have been improved as compared with the one shown in FIG. 1 in that it is no longer necessary for the operator to turn his or her eyes away from the needle, the machine is no different from the one shown in FIG. 1 in that in order to operate the lever D, it is necessary for the operator to shift one of his or her two hands placed on the cloth to the lever D. Moreover, in the case of this machine, the addition of the lever D results in the operating parts being distributed at two places, and it can hardly be said from the standpoint of operation that this apparatus is simplified. Further, constituting said buttons by machanical buttons makes it difficult to arrange them as desired, in consideration of the space of the machine. If an arrangement wherein the stop button is located adjacent the base of the needle in order to make it possible to stop the machine without shifting the hand placed on the cloth during sewing operation is applied to the machine shown in FIG. 1, it is necessary to mechanically interlock the speed selection buttons, which, in this case, should also act as start switches, with the stop button located away from said speed selection buttons so that a stop instruction operation by the stop button will reset the speed selection button. This has the disadvantage of complicating the apparatus. Further, in the sewing machine so designed that its rotation is controlled by button operation, a danger can occur that a button is accidentally held depressed as the sewing machine is taken out of its receptacle, without the knowledge of the operator, who then turns on the power, whereupon the machine is accidentally started. In order to prevent this, it is necessary to provide a complicated safety circuit such as disclosed in Japanese Patent Lay-Open No. 61,351/76. Thus, the apparatus will be complicated also from this point of view.